Inhibition of apolipoprotein B100 secretion by lipid-induced hepatic endoplasmic reticulum stress in rodents

J Clin Invest. 2008 Jan;118(1):316-32. doi: 10.1172/JCI32752.

Abstract

ER stress can cause hepatic insulin resistance and steatosis. Increased VLDL secretion could protect the liver from ER stress-induced steatosis, but the effect of lipid-induced ER stress on the secretion of VLDL is unknown. To determine the effect of lipids on hepatic ER stress and VLDL secretion, we treated McA-RH7777 liver cells with free fatty acids. Prolonged exposure increased cell triglycerides, induced steatosis, and increased ER stress. Effects on apoB100 secretion, which is required for VLDL assembly, were parabolic, with moderate free fatty acid exposure increasing apoB100 secretion, while greater lipid loading inhibited apoB100 secretion. This decreased secretion at higher lipid levels was due to increased protein degradation through both proteasomal and nonproteasomal pathways and was dependent on the induction of ER stress. These findings were supported in vivo, where intravenous infusion of oleic acid (OA) in mice increased ER stress in a duration-dependent manner. apoB secretion was again parabolic, stimulated by moderate, but not prolonged, OA infusion. Inhibition of ER stress was able to restore OA-stimulated apoB secretion after prolonged OA infusion. These results suggest that excessive ER stress in response to increased hepatic lipids may decrease the ability of the liver to secrete triglycerides by limiting apoB secretion, potentially worsening steatosis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apolipoprotein B-100 / metabolism*
  • Cell Line
  • Endoplasmic Reticulum / metabolism*
  • Endoplasmic Reticulum / pathology
  • Fatty Acids, Nonesterified / toxicity*
  • Fatty Liver / chemically induced
  • Fatty Liver / metabolism*
  • Fatty Liver / pathology
  • Insulin Resistance
  • Lipoproteins, VLDL / metabolism
  • Liver / metabolism*
  • Liver / pathology
  • Mice
  • Oleic Acid / toxicity*
  • Proteasome Endopeptidase Complex / metabolism
  • Stress, Physiological / chemically induced
  • Stress, Physiological / metabolism
  • Stress, Physiological / pathology
  • Time Factors
  • Triglycerides / metabolism

Substances

  • Apolipoprotein B-100
  • Fatty Acids, Nonesterified
  • Lipoproteins, VLDL
  • Triglycerides
  • Oleic Acid
  • Proteasome Endopeptidase Complex